<p>Site-specific recombination plays an important role in DNA rearrangement in prokaryotic organisms. Two types of site-specific recombination are known to occur:</p><ol><li>Recombination between inverted repeats resulting in the reversal of a DNA segment.</li><li>Recombination between repeat sequences on two DNA molecules resulting in their cointegration, or between repeats on one DNA molecule resulting in the excision of a DNA fragment.</li></ol><p>Site-specific recombination is characterised by a strand exchange mechanism that requires no DNA synthesis or high energy cofactor; the phosphodiester bond energy is conserved in a phospho-protein linkage during strand cleavage and re-ligation.</p><p>Two unrelated families of recombinases are currently known [<cite idref="PUB00001148"/>]. The first, called the 'phage integrase' family, groups a number of bacterial phage and yeast plasmid enzymes. The second [<cite idref="PUB00003786"/>], called the 'resolvase' family, groups enzymes which share the following structural characteristics: an N-terminal catalytic and dimerization domain that contains a conserved serine residue involved in the transient covalent attachment to DNA <db_xref db="INTERPRO" dbkey="IPR006119"/>, and a C-terminal helix-turn-helix DNA-binding domain. </p> Resolvase, helix-turn-helix domain